The present invention relates to a sweeping unit for mounting on a carrier vehicle or on a trailer, comprising a carrying frame and at least one motor-driven rotary brush mounted in the carrying frame such that it can be rotated about its longitudinal axis, the carrying frame having supporting wheels, of which the vertical distance from the axis of the rotary brush can be changed by means of an adjusting unit, which comprises at least one hydraulic adjusting cylinder and a control apparatus.
Various designs of sweeping units of the type specified above are known, for example from European Patent 0372258 and German Offenlegungsschrift 3740215. Also known are sweeping units which have a construction essentially of a generic type, but differ therefrom in that a hydraulic adjusting cylinder, rather than being set via control apparatus, is part of a hydraulic regulating circuit, and in that, furthermore, a carrying frame does not have supporting wheels. Sweeping units of this type are disclosed in, for example, German Offenlegungsschriften 2455200 and 2821627 and European Patent Applications 0189371 and 0843047.
For all the sweeping units known from the publications specified above, correct setting of sweeping-level width is extremely important for an efficient sweeping operation which, at the same time, does not adversely affect the materials. Thus, as is explained in detail in European Patent 0372258, an optimum sweeping-level width is characterized by a good cleaning result with a low level of bristle wear. If the sweeping-level width is below the optimum value, cleaning capacity can noticeably decrease. With a sweeping-level width above the optimum value, in contrast, bristle wear noticeably increases without any notable improvement to cleaning result.
It is not possible with any of the sweeping units known from the publications specified above for the sweeping-level width to be set with the desired level of accuracy. This applies particularly to the prior art according to the generically determinative documents. It is to be taken into consideration in this context that, with a conventional rotary brush of a diameter of 914 mm, a height adjustment of 1 mm means a change in sweeping level of approximately 60 mm. The fact that values of between 60 mm and 100 mm are considered as a suitable sweeping-level width makes it clear which requirements are to be met in practice by the accuracy of the adjusting unit.
Against the backdrop of the prior-art disadvantage explained above, the object of the present invention is to provide a sweeping unit of the generic type in which an optimum sweeping level can be set with a high level of accuracy.
This object is achieved according to the present invention in that hydraulically connected to at least one adjusting cylinder is a supply cylinder having a piston, or other signal generator, connected to a counting and/or displacement measuring device connected to a control apparatus, or a mechanical adjusting drive. The supply cylinder has a hydraulic operating chamber which communicates with the at least one adjusting cylinder and has a smaller cross-sectional surface area than the at least one adjusting cylinder.
The supply cylinder effects volumetric proportioning of hydraulic fluid to the at least one adjusting cylinder, this corresponding to advancement movement of the at least one adjusting cylinder from a reference position into an operating position, which corresponds to the optimum sweeping-level width. The reference position here may correspond to various characteristic positions of the rotary brush, relative to the surface which is to be cleaned, with reference to which the control apparatus calculates an advancement movement of the at least one adjusting cylinder which is necessary in order to bring the rotary brush into the operating position, which is characterized by the optimum sweeping-level width. An initial ground-contact position of the rotary brush and the corresponding position of the at least one adjusting cylinder are particularly preferably used as the reference position because this automatically compensates for bristle wear (see below). A bypass line to the supply cylinder is particularly preferably provided since the supply cylinder is required merely for the precise lowering of the rotary brush from its ground-contact position into its operating position. There is no need for a volumetric determination of the hydraulic-fluid volume which is fed to the at least one adjusting cylinder or flows out of the same, either during lowering of the rotary brush into the ground-contact position or during raising of the rotary brush, respectively. The above-mentioned configuration of a hydraulic system with the supply cylinder results in it being possible for the at least one adjusting cylinder to be set particularly precisely.
Although it is conceivable, within the context of the above-mentioned development of the present invention, for a mechanical adjusting drive to act on the piston of the supply cylinder, with the result that the supply cylinder itself performs the function of a pump, it is particularly preferable for the supply cylinder to be connected between a hydraulic pump and the at least one adjusting cylinder. It follows along in this case, the volume of the hydraulic fluid fed to the at least one adjusting cylinder being determined by the number of strokes of the supply cylinder and/orxe2x80x94in the case of incomplete strokesxe2x80x94by the displacement of the piston of the supply cylinder.
According to another preferred development of the invention, there is provided a sensor which senses a driving torque or a driving power of the rotary brush, or a variable linked thereto. A signal from the sensor is connected to the control apparatus, and the control apparatus determines the operating position of the adjusting element. The operation position corresponding to the optimum sweeping-level width is set as a function of the ground-contact position of the adjusting element. The ground-contact position is determined during lowering of the rotary brush, by an abrupt rise of the sensor signal.
In the sweeping unit developed in this way, the actual rotary-brush diameter, which is dependent on the bristle wear, is automatically taken into account for setting the position of the rotary brush relative to the surface which is to be cleaned, in that during the individual sweeping operation, the ground contact of the rotary brush and the corresponding ground-contact position of the adjusting element are used as reference points for the operating position of the adjusting element, the operating position corresponding to the optimum sweeping-level width. The ground contact of the rotary brush, during lowering of the latter, is determined here by an abrupt rise of the sensor signal which is emitted by the sensor which senses the driving torque or the driving power of the rotary brush or a variable linked thereto.
Problems known to occur with sweeping units according to the prior art do not arise in a sweeping unit as described above. Unlike the case in German Offenlegungsschriften 2455200 and 2821627 and in EP-A 0189371 and 0843047, the sweeping-level width set by the control apparatus is not dependent on the surface conditions, in particular the roughness of the surface which is to be cleaned, nor, unlike the case in EP-B 0372258 and in German Offenlegungsschrift 3740215, is a complicated measuring-sensor arrangement which is susceptible to malfunctioning necessary. Nevertheless, the setting of the sweeping-level width is based not on an average degree of rotary-brush wear, which is dependent on the running performance of the relevant rotary brush, but on the actual degree of wear. Consequently, this development of the invention provides a sweeping unit in which the optimum sweeping level can automatically be set precisely with extremely low outlay on apparatus. The sweeping unit of the present invention is thus distinguished by a robust construction which is not susceptible to malfunctioning.
The above-described development of the invention can advantageously be used if the operating position of the adjusting element is determined, in the control apparatus, from the ground-contact position or other reference position of the adjusting element by the addition of a constant variable. In this case, in other words, the rotary brush, during the sweeping operation, would be lowered in each case into a position which is located a certain distance (e.g. 2 mm) below the ground-contact position. Although, as a result of the geometrical relationships, this would result, with continuing wear of the rotary brush, in a gradual reduction in the sweeping-level width, it would be compensatedxe2x80x94at least partiallyxe2x80x94by an increasing hardness of the brush, so that the cleaning result would essentially stay the same.
In contrast, however, another preferred development is distinguished in that an adjusting-element advancement movement, by means of which the operating position of the adjusting element differs from the ground-contact position thereof, is dependent on the actual diameter of the rotary brush. In this case, the control apparatus comprises a corresponding compensation circuit, for example in the form of a characteristic curve, which specifies the advancement movement, i.e. the difference between the operating position and ground-contact position of the adjusting element, in dependence on an actual diameter of the rotary brush. The actual diameter may be derived directly from the ground-contact position of the adjusting element sincexe2x80x94with supporting wheels resting on the surface which is to be cleanedxe2x80x94each diameter of the rotary brush has precisely one ground-contact position of the adjusting element corresponding to it. Other suitable measuring devices which are intended for determining the diameter of the rotary brush, and likewise evaluate the position of the rotary brush relative to the carrying frame in the ground-contact position of the rotary brush, can be used in the same way. These include, in particular, an angle-measuring instrument which determines an angular position of at least one carrying arm of the rotary brush relative to a further component of the carrying frame. The critical factor is that the diameter of the rotary brush, rather than being measured directlyxe2x80x94via sensorsxe2x80x94in each case, is derived from the position of the rotary brush at the moment at which it comes into contact with the ground, and thus indirectly utilizing the signal of the ground-contact sensor.